Coming on strong: Gerard Butler muscles his way into Frank Miller’s ‘300’

In “300,” the violent big-screen re-creation of Frank Miller’s (“Sin City”) graphic novel opening Friday, Gerard Butler plays a Spartan king who leads 300 of the ancient world’s most fearsome fighters into a battle to the death with a Persian force numbering 250,000.

No stranger to physically challenging roles, Butler and his toned six-pack abs are on constant display in a costume that consists of boots, a scarlet cape and what resembles a sleek black leather swimsuit.

“When I went into this film I was in really bad shape - trust me,” said Butler, who felt compelled to match the elite crew of 50 stuntmen throughout filming.

“I had just come from Italy and three different people who I had never met before had commented on me being fat, because I have this kind of stomach that, if it’s relaxed, I can do an ‘Alien’ impersonation. John Hurt, like in ‘Alien,’ right?”

With that, Butler stood, pulled up his T-shirt and with a cheeky “Check this out,” proceeded to roll his flattened stomach out into a sizable ball. For a minute, it looked as if an alien might pop out.

He’d never sung until he landed “Phantom of the Opera.” For “300,” he promised Warner Brothers executive Alan F. Horn that if he was cast as King Leonidas, “I will so kick a-- that I will make this my life - and I did, because that’s what I do.”

“I went a little crazy,” he said. That meant six days per week of solid training for three months before filming began. Then he changed routines and continued for another two months while working 16-hour days.

Maybe it’s the work that keeps this romantic leading man so spectacularly single - at least in the public eye.

“I’m gay,” he said, then laughing. “No, I’m joking.”

How has he managed to remain a bachelor?

“Actually, I keep my very personal life personal. I’m pretty good about being open and talking, but I think that I don’t let many people in that much. I’ve always been that way,” he said. “But actually I was in quite a long relationship up until very recently.”